It shows correctly if I create an appointment in August, was that for any day/time (or a specific day/date time) in August that you had the problem? Which version of Zimbra/Browser/Operating System are you using?

No, I'm afraid I can't duplicate this at all. I seem to have tried every date/time combination I could think of, I even changed the timezone to Paris (I normally have all my systems at GMT) but nothing seems to cause it to fail. I guess we'll have to wait for one of the Zimbra guys to help, I can't think of anything else to suggest.

open the debug pop up by entering "$set:debug 3" into the search bar. then set the appointment. some communication between the browser and the server will show in the pop up. copy everything in there and post it or pm it to me.